The distribution of helicity and intense convection in tropical cyclones

Tropical cyclones embedded in environments of moderate to strong vertical wind shear (>10 m s-1) have been shown to maintain their intensity for 24-48 hours after the onset of shear. The distribution of precipitation in these storms is highly asymmetric with intense eyewall convection preferentially occurring downshear and left of the ambient vertical wind shear vector. A recent observational study employing dropsonde data from Hurricane Bonnie (1998) showed that helicity (the scalar product of the three-dimensional velocity and vorticity vectors) is also maximized in the downshear left quadrant. Values exceeded those associated with continental severe weather outbreaks. In Bonnie, deep, intense convective cells, resembling mid-latitude supercells, repeatedly formed in the downshear left quadrant. It was hypothesized that these long-lived cells helped the vortex maintain its intensity in the presence of shear exceeding 12 m s-1. In this presentation, we will examine the azimuthal and radial distribution of helicity, convective available potential energy and intense convection in tropical cyclones simulated with the Advanced Hurricane WRF (AHW) model. By examining a large number of simulated storms, it is anticipated a greater understanding of the dynamics of tropical cyclone vortices in shear will be gained.